This was partly because letters also served as instruction codes with some mnemonic aspects to them. (This is also found on early Univacs. Coincidentally, Stan Frankel, the designer of the LGP-30, came from Eckert’s and Mauchly’s team.)
As in:
b - bring from memory (load into AC)
h - hold and store (deposit AC in memory)
c - clear and store (deposit AC and set it to zero)
y - store address (store AC as operand)
u - unconditional transfer (jump)
r - return address (stores PC+2 as operand at given address)
t - test (conditional transfer on AC negative)
z - stop (break point in operand)
p - print
i - input
a - add
s - subtract
m - multiply (most significant bits of result in AC)
n - multiply (least significant bits of result in AC)
d - divide
e - extract (mask, logical AND)
This left only a limited set for hexadecimal encoding, namely f, g, j, k, q, w. (And yes, "l" is 1, since Flexowriters weren't invented as computer terminals, rather they are electric typewriters with a potential for automatization.)
Since hexadecimal was used for operands, which were actually addresses on the magnetic drum given by track and sector numbers in binary, which in turn resulted in a rather interesting single-word instruction format, this further complication may not have mattered much.
As in:
This left only a limited set for hexadecimal encoding, namely f, g, j, k, q, w. (And yes, "l" is 1, since Flexowriters weren't invented as computer terminals, rather they are electric typewriters with a potential for automatization.)Since hexadecimal was used for operands, which were actually addresses on the magnetic drum given by track and sector numbers in binary, which in turn resulted in a rather interesting single-word instruction format, this further complication may not have mattered much.
Compare https://www.masswerk.at/nowgobang/2019/lgp-30